Fix for task dates update (#24)

.drone.yml

@@ -9,14 +9,15 @@ clone:
 
 pipeline:
   build:
-    image: node
+    image: node:11-alpine
     pull: true
     group: build-static
     commands:
-      - npm install
-      - npm run lint
+      - apk add yarn
+      - yarn
+      - yarn run lint
       - "echo '{\"VIKUNJA_API_BASE_URL\": \"/api/v1/\"}' > /srv/app/src/git.kolaente.de/vikunja/frontend/public/config.json" # Override config
-      - npm run build
+      - yarn run build
     when:
       event: [push, tag, pull_request]